The present invention generally relates to a chair that includes a seat and a backrest, wherein the seat includes a front part which is carried by a seat base structure, and a rear seat part which borders on the front seat part along a join line which extends generally perpendicularly to a chair symmetry plane, wherein the chair includes means for selectively setting or adjusting the distance between the seat join line and the backrest so that a chair user sitting on the seat with his back in contact with the backrest can take a sitting position in which his hip joints lie generally in a vertical plane that includes the join line, and wherein means are provided for moving the rear seat part vertically in relation to the front seat part.
A chair of this kind is known from an International Application Number WO 97/10735 published under the Patent Cooperation Treaty.
The invention thus relates to a chair of the kind which includes a seat and a backrest, wherein the seat includes a front part which is supported by a chair base, and a rear part which borders on the front part of the seat along a join line which extends generally parallel with the intersection between the seat and the backrest, wherein means are provided for selectively adjusting the horizontal distance between the seat join line and the backrest, and wherein means are provided for moving the rear seat part vertically relative to the front seat part.
The user of such a chair adjusts the distance between the backrest and the join line so that a vertical plane through the hip joints of the user will coincide generally with the join line, when the user rests his back against the backrest with his upper body generally straight and with his buttocks seated on the chair seat.
Assuming that the upper surfaces of the rear and the front seat parts lie generally in one and the same plane, i.e. are essentially flush with one another, most of the user""s weight will be supported by the rear part of the seat.
When the rear part of the seat is lowered, a large part of the earlier load on the rear part of the seat (or the whole of the load) is likely to be transferred to the front part of the seat. Because the join line is set so as to coincide with the vertical plane through the wearer""s hip joints (or immediately beneath the ischial tuberosities), the increase in weight will not result in any upward rotary force against the user""s thighs. The friction between the backrest of the chair and the user""s spine will take-up part of the user""s weight.
That part of the user""s buttocks supported by the rear part of the seat is now able to sag and therewith subject the lumbar region of the wearer""s back to traction.
By restricting vertical downward movement of the rear part of the seat, the user is able to adjust the seat for desired traction of the lumbar region and/or to adjust the chair for desired transfer of load form the rear part of the seat to its front part.
The object of the present invention is to provide a simple construction which can be readily manufactured and easily fitted and which can be easily maneuvered by the mechanism that supports the rear part of the chair seat. Another object is to provide a construction which can be readily fitted to a typical chair base, for instance of the kind which enables the chair to be tilted, raised, twisted or moved in some other way relative to the chair support base.
These objects are achieved with a chair that includes a seat and a backrest. The seat includes a front part carried by a seat base structure, and a rear seat part which borders on the front seat part along a join line. The join line extends generally perpendicularly to a chair symmetry plane. The chair includes means for selectively setting or adjusting the distance between the seat join line and the backrest so that a chair user sitting on the seat with his back in contact with the backrest can take a sitting position in which his hip joints lie generally in a vertical pane that includes the join line. Means are provided for moving the rear seat part vertically in relation to the front seat part. The vertical movement means include a lever which is pivotally mounted on the front seat part and which supports the rear seat part for vertical movement.
Also, there is a blocking device which is adapted to operate between the lever and a support point which is stationary relative to the front seat part. The blocking device (14) has a variable length and in one terminal position functions to cause the lever to hold the rear seat part flush with the front seat part. A trigger mechanism, when actuated manually, causes the length of the blocking device to be reduced and therewith lower the rear seat part in relation to the front seat part.
Further embodiments of the inventive chair are that the lever is a bell-crank lever, and the blocking device is orientated to establish a length variation generally in a horizontal direction parallel with the chair symmetry plane.
Additionally, the blocking device is a gas spring that includes a latching device and a mechanical spring which acts in a direction in which it strives to return the rear seat part to the same level as that occupied by the front seat part.
The gas spring comprises a cylinder that includes a piston having a valve means. The piston is connected to a piston rod. The lever is a bell-crank lever which includes an arm that extends downwardly from the pivot point. The cylinder of the gas spring is pivotally mounted on a pivot point at the free end of the lever arm, and the piston rod of the gas spring is fixedly connected to the support point. The latching means includes a rod that extends coaxially through the piston rod and projects out from the free end of the piston rod. A trigger mechanism is pivotally mounted on the front seat part to permit the rear seat part to be lowered when activated.
In preferred embodiments of the invention, the longitudinal axis of the blocking device extends generally parallel with the longitudinal axis of the chair. The blocking device may consist of a gas spring which is spring-biased so as to return the rear part of the seat to its terminal position in which it lies flush with the front part of the seat, in the absence of load on the rear part of the seat and upon activation of the trigger mechanism. The gas spring will conveniently include a valve means which can be activated by the trigger mechanism and which separates the primary gas-pressure applying chamber of the gas spring from the secondary gas chamber thereof. The through-passage of the open valve may be adapted to restrict the speed at which the piston rod/piston of the gas spring moves in relation to the cylinder part of the spring.
By suspending the rear part of the seat from a so-called bell-crank lever which is pivotally mounted on the front part of the seat, the means for moving the rear part of the seat vertically can be given a small structural height and can be supported by the front part of the seat.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.